NK T cells are a lymphocyte subset that is characterized by the expression of an invariant Valpha-Jalpha T cell antigen receptor (TCR), autoreactivity to CD1 molecules, and the ability to rapidly produce large amounts of IFNgamma and/or IL-4 following stimulation. On account of their invariant TCR repertoire and their ability to rapidly make cytokines, NK T cells may be considered to be part of the innate immune response. Consistent with an important role for this subset in immune regulation, recent stimulate anti-tumor immune responses. We have shown that human NK T cells can recognize data strongly suggest that NK T cells could prevent the progression to diabetes, and that they can the marine sponge-derived lipoglycan, a-galactosyl ceramide (alpha-Ga1Cer), when it is presented by the human CD1 molecule (hCD1d). In the proposed experiments, we will use in vitro hCD1d binding data, site directed mutagenesis of CD1, and immune assays to define what chemical groups of the alpha-GalCer lipoglycan are required for hCD1 d binding and TCR recognition. We will determine if different lipoglycan antigens induce different cytokine profiles from NK T cells. We also will identify the natural counterpart of this marine sponge lipoglycan antigen, which is required for hCD1d autoreactivity in mouse and human cells. We will determine if the expression or presentation of this autologous lipoglycan is caused by the induction of cell death, which would suggest that NK T cells are a surveillance system for dead cells. Finally, we will determine the avidity of the interaction of the NK T cell TCR for CD1d plus antigen, and the important contact point on the a chain of the TCR for hCd1d plus antigen. Recognition of autologous lipoglycans by NK T cells represents a new paradigm for T cell antigen recognition at both the structural and functional levels. The proposed experiments will delineate the molecular basis for this type of antigen recognition, and by testing the response of NK T cells to different compounds, they may provide strategies for the augmentation and regulation of this important category of T cell responses.